Power generation system

ABSTRACT

A power generation system includes a shroud that defines a fluid flow path. A compressor is in the fluid flow path, and a combustor is in the fluid flow path downstream from the compressor. A turbine is in the fluid flow path downstream from the compressor and the combustor. An electric generator is in the fluid flow path upstream from the compressor, and the electric generator includes a rotor coaxially aligned with the turbine.

FIELD OF THE INVENTION

The present invention generally involves a power generation system.Particular embodiments of the power generation system may be used as aportable power supply or incorporated into an aircraft propulsion systemto generate sufficient electric output to power a turboprop or turbofanengine.

BACKGROUND OF THE INVENTION

Conventional aircraft propulsion systems often include a gas turbineengine that produces thrust and mechanical power. The gas turbine enginegenerally includes a compressor, one or more combustors downstream fromthe compressor, and a turbine downstream from the combustor(s). Ambientair enters the compressor as a working fluid, and one or more stages ofrotating blades and stationary vanes in the compressor progressivelyincrease the pressure of the working fluid. The working fluid exits thecompressor and flows to the combustors where it mixes with fuel andignites to generate combustion gases having a high temperature,pressure, and velocity. The combustion gases flow to the turbine wherethey produce work by rotating the turbine before exhausting from theturbine to provide thrust. A spool or shaft connects the turbine to apropulsor, such as a propeller or a fan, so that rotation of the turbinedrives the propulsor to generate additional thrust. The spool or shaftmay also connect the turbine to a rotor of an electric generator locatedinside the fuselage of the aircraft. In this manner, the gas turbineengine may also drive the rotor to produce sufficient electricity topower the hotel loads of the aircraft.

The output power of the electric generator is a function of the size ofthe rotor and the strength of the magnetic field associated with theelectric generator. Specifically, increasing the size of the rotorand/or the strength of the magnetic field increases the output power ofthe electric generator. However, increasing the size of the rotor and/orincorporating larger permanent magnets on the rotor produces largercentrifugal forces that tend to separate the permanent magnets from therotor, particularly at the high rotational speeds associated with asingle-spool gas turbine engine that directly drives the rotor of theelectric generator. Although multiple spools or shafts, gears, and/ortransmissions may be used to reduce the centrifugal forces by reducingthe rotational speed of the rotor, the additional weight and supportsystems associated with multiple spools or shafts, gears, and/ortransmissions may be undesirable, particularly in aircraft applications.Therefore, the need exists for a power generation system that can bedriven by a gas turbine engine to generate 1 MW, 1.5 MW, 2 MW, or moreof electric power without requiring multiple spools or shafts, gears,and/or transmissions.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention are set forth below in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

One embodiment of the present invention is a power generation systemthat includes a shroud that defines a fluid flow path. A compressor isin the fluid flow path, and a combustor is in the fluid flow pathdownstream from the compressor. A turbine is in the fluid flow pathdownstream from the compressor and the combustor. An electric generatoris in the fluid flow path upstream from the compressor, and the electricgenerator includes a rotor coaxially aligned with the turbine.

An alternate embodiment of the present invention is a power generationsystem that includes a gas turbine engine having a compressor, acombustor downstream from the compressor, and a turbine downstream fromthe combustor. An electric generator is coaxially aligned with thecompressor, and the electric generator includes a rotor coaxiallyaligned with the turbine. A shaft connects the turbine of the gasturbine engine to the rotor of the electric generator so that theturbine and the rotor rotate at the same speed. The electric generatorincludes structure for holding a plurality of permanent magnets in placeon the rotor of the electric generator during operation of the turbine.

In yet another embodiment of the present invention, a power generationsystem includes a gas turbine engine having a compressor, a combustordownstream from the compressor, and a turbine downstream from thecombustor. An electric generator is coaxially aligned with the turbine,and the electric generator includes a rotor. A shaft connects theturbine of the gas turbine engine to the rotor of the electric generatorso that the turbine and the rotor rotate at the same speed. A pluralityof rails extend radially from the rotor of the electric generator, and aplurality of permanent magnets are engaged with the plurality of rails.

Those of ordinary skill in the art will better appreciate the featuresand aspects of such embodiments, and others, upon review of thespecification.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof to one skilled in the art, is set forth moreparticularly in the remainder of the specification, including referenceto the accompanying figures, in which:

FIG. 1 is side cross-section view of a gas turbine propulsion systemthat includes a power generation system according to one embodiment ofthe present invention;

FIG. 2 is an enlarged side cross-section view of the gas turbine engineand electric generator shown in FIG. 1;

FIG. 3 is an enlarged front perspective cross-section view of theelectric generator shown in FIG. 1;

FIG. 4 is an axial cross-section view of the rotor of the electricgenerator taken along line A-A of FIG. 3 according to one embodiment ofthe present invention;

FIG. 5 is an axial cross-section view of the rotor of the electricgenerator taken along line A-A of FIG. 3 according to an alternateembodiment of the present invention;

FIG. 6 is an axial cross-section view of the rotor of the electricgenerator taken along line A-A of FIG. 3 according to an alternateembodiment of the present invention;

FIG. 7 is an axial cross-section view of the rotor of the electricgenerator taken along line A-A of FIG. 3 according to an alternateembodiment of the present invention;

FIG. 8 is an enlarged side cross-section view of the electric motor andpropulsor shown in FIG. 1; and

FIG. 9 is an enlarged front perspective cross-section view of theelectric motor and propulsor shown in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to present embodiments of theinvention, one or more examples of which are illustrated in theaccompanying drawings. The detailed description uses numerical andletter designations to refer to features in the drawings. Like orsimilar designations in the drawings and description have been used torefer to like or similar parts of the invention. Each example isprovided by way of explanation of the invention, not limitation of theinvention. In fact, it will be apparent to those skilled in the art thatmodifications and variations can be made in the present inventionwithout departing from the scope or spirit thereof. For instance,features illustrated or described as part of one embodiment may be usedon another embodiment to yield a still further embodiment. Thus, it isintended that the present invention covers such modifications andvariations as come within the scope of the appended claims and theirequivalents.

As used herein, the terms “first,” “second,” and “third” may be usedinterchangeably to distinguish one component from another and are notintended to signify location or importance of the individual components.As used herein, the terms “upstream” and “downstream” refer to thelocation of items with reference to the direction of fluid flow in afluid pathway. For example, item A is “upstream” from item B and item Bis downstream from item A if fluid normally flows from item A to item B.As used herein, “axial” refers to the direction of the longer axis of acomponent, “radial” refers to the direction perpendicular to the axialdirection, and “circumferential” refers to the direction around acomponent.

Embodiments of the present invention include a power generation systemthat can be driven by a gas turbine engine to generate 1 MW, 1.5 MW, 2MW, or more of electric power without requiring multiple spools orshafts, gears, and/or transmissions. The power generation system may beincorporated into any vehicle and/or used as a portable power supply forgeographically remote areas or following a natural disaster. Forexample, the power generation system may be housed in a nacelle andattached to the fuselage or wing of an aircraft. The power generationsystem generally includes a gas turbine engine and an electricgenerator. The gas turbine engine generally includes a compressor, acombustor, and a turbine, and the gas turbine engine drives the electricgenerator to produce electricity that may provide a portable powersupply. Alternately or in addition, the electricity produced by theelectric generator may be used to power a propulsor, such as a propelleror a fan enclosed by a shroud or cowling. In this manner, the propulsormay be rotationally isolated from the gas turbine engine so thatrotation of the propulsor is completely independent from operation ofthe gas turbine engine. As used herein, the phrase “rotationallyisolated” means that no mechanical coupling exists between twocomponents to transfer rotation between the two components, in thiscase, the gas turbine engine and the propulsor. As a result, rotation ofthe propulsor is completely independent from operation of the gasturbine engine, allowing each to operate at its most efficient speedindependently from the other.

Particular embodiments of the present invention may include additionaldesign features to reduce the weight, manufacturing cost, and/ormaintenance associated with the gas turbine engine. For example, the gasturbine engine may be a single-spool gas turbine engine. As used herein,a “single-spool gas turbine engine” means a gas turbine engine in whicha single spool or shaft, which may include multiple segments, connectsthe turbine to the compressor so that the turbine and compressor rotateat the same speed. The single spool or shaft may also connect the gasturbine engine to the electric generator so that the turbine andelectric generator rotate at the same speed. The use of a single spoolor shaft reduces the weight and parts associated with the gas turbineengine, simplifying manufacture, maintenance, and repairs compared tomulti-spool and/or geared systems. In addition, the reduced weightassociated with a single-spool gas turbine engine reduces the need for aseparate lube oil system to lubricate and cool the rotating componentsof the gas turbine engine. As a result, in particular embodiments thegas turbine engine may include non-lubricated bearings and/or anintegrally bladed rotor that further reduce manufacturing, maintenance,and repair costs. As used herein, “non-lubricated bearings” means thatthe bearings are not supplied external lubrication, such as from a lubeoil system, during operation of the gas turbine engine.

FIG. 1 provides a side cross-section view of a gas turbine propulsionsystem 10 that includes a power generation system 11 according to oneembodiment of the present invention. In the particular embodiment shownin FIG. 1, the gas turbine propulsion system 10 includes a gas turbineengine 12, an electric generator 14, an electric motor 16, and apropulsor 18. The power generation system 11 generally includes the gasturbine engine 12 and the electric generator 14. As will be described inmore detail, the electric motor 16 and propulsor 18 are rotationallyisolated from the gas turbine engine 12 so that the propulsor 18 rotatesindependently from operation of the gas turbine engine 12 at all times.A shroud 20 supported by struts 22 may surround the gas turbine engine12 and propulsor 18 to define a fluid flow path 24 from the propulsor 18to the gas turbine engine 12. If present, the shroud 20 focuses theairflow produced by the propulsor 18 that enters the gas turbine engine12, as well as the airflow that bypasses the gas turbine engine 12 andexits the shroud 20 as thrust.

FIG. 2 provides an enlarged side cross-section view of the gas turbineengine 12 and electric generator 14 shown in FIG. 1. In the particularembodiment shown in FIGS. 1 and 2, the gas turbine engine 12 is locatedin the fluid flow path 24 downstream from the propulsor 18. The gasturbine engine 12 generally includes a compressor 26, combustors 28downstream from the compressor 26, and a turbine 30 downstream from thecombustors 28, as is known in the art. The compressor 26 includes arotor 32 with one or more alternating stages of rotating blades 34 andfixed vanes 36 that progressively increase the pressure of the workingfluid entering the compressor 26. The combustors 28 mix the compressedworking fluid with fuel and ignite the mixture to generate combustiongases having a high temperature, pressure, and velocity. The turbine 30includes a rotor 38 with one or more alternating stages of rotatingblades 40 and fixed vanes 42 to extract work from the combustion gasesexiting the combustors 28. In the particular embodiment shown in FIGS. 1and 2, the compressor 26 is a single stage, axial-flow compressor, andthe turbine 30 is a two-stage axial-flow turbine. However, unlessspecifically recited in the claims, the gas turbine engine 12 includedin the present invention is not limited to any particular design or sizeand may include a multi-stage axial or radial-flow compressor 26, one ormore combustors 28, and an axial or radial-flow turbine 30 with one ormore stages.

Gas turbine engines are generally more efficient at higher turbine inlettemperatures which may damage the rotating blades in the turbine. As aresult, the rotating blades are often hollow so that cooling may besupplied through the rotor to the hollow rotating blades to preventdamage from the higher turbine inlet temperatures. In the presentinvention, the rotational isolation between the gas turbine engine 12and the propulsor 18 allows the gas turbine engine 12 to operate atlower turbine inlet temperatures than what may otherwise be preferred toachieve a desired efficiency for the gas turbine engine 12. The lowerturbine inlet temperatures in turn reduce the need for internal coolingto the rotating blades 40 in the turbine 30. As a result, in particularembodiments of the present invention, the rotor 38 in the turbine 30 maybe an integrally bladed rotor 38 or “blisk” in which the rotating blades40 are solid and integrally formed as a solid piece with the rotor 38.The integrally bladed rotor 38 may be manufactured by additive printing,casting, machining from a solid piece of material, or welding individualblades 40 to the rotor 38, as is known in the art. The resultingintegrally bladed rotor 38 reduces the complexity, weight, and cost ofmanufacturing and assembly by avoiding the intricacy of hollow blades,dovetail connections to the rotor, and forced cooling through the rotorand blades.

The gas turbine engine 12 may include one or more spools or shafts thatrotationally couple the turbine 30 to the compressor 26, as is known inthe art. In a multi-spool gas turbine engine, for example, thecompressor and the turbine may each include a high pressure stage and alow pressure stage, and a first spool may connect the high pressurestage of the turbine to the high pressure stage of the compressor, whilea second spool may connect the low pressure stage of the turbine to thelow pressure stage of the compressor. In this manner, each turbine stagedrives the corresponding compressor stage with a separate spool, withone spool inside the other spool.

In the particular embodiment shown in FIGS. 1 and 2, the gas turbineengine 12 is a single-spool gas turbine engine 12 in which a singlespool or shaft 44 connects the turbine 30 to the compressor 26. Thesingle spool or shaft 44 may include multiple segments connectedtogether to rotate in unison and transmit rotation of the turbine rotor38 directly to the compressor rotor 32 without the use of gears.

The single-spool gas turbine engine 12 shown in FIGS. 1 and 2 is lighterand generates less heat compared to a similarly-sized gas turbine enginewith multiple spools or shafts and/or gears. As a result, bearings thatsupport the rotating components of the gas turbine engine 12 do notrequire an external source of lube oil to lubricate and cool thebearings, and particular embodiments of the present invention mayinclude non-lubricated bearings 46 that rotatably support the shaft 44or single-spool gas turbine engine 12. As shown most clearly in FIG. 2,for example, the non-lubricated bearings 46 may support the single spoolor shaft 44 at various positions in the gas turbine engine 12 and/orelectric generator 14. The non-lubricated bearings 46 may include, forexample, air-lubricated bearings or ceramic bearings encapsulated in acasing that allows periodic addition of lubrication to the bearingswithout the ability to permit lube oil flow through the bearings duringoperation. The non-lubricated bearings 46 thus further reduce theweight, manufacturing cost, maintenance cost, and complexity of the gasturbine engine 12 by obviating the need for a separate lube oil systemand associated pumps, sumps, and filters.

FIG. 3 provides an enlarged front perspective cross-section view of theelectric generator 14 shown in FIGS. 1 and 2. The electric generator 14generally includes a rotor 48 and a stator 50, and relative movementbetween the rotor 48 and the stator 50 disrupts a magnetic field betweenthe two to convert mechanical energy into electrical energy, as is knownin the art. In the particular embodiment shown in FIGS. 2 and 3, therotor 48 includes permanent magnets 52 that create the magnetic field,and the stator 50 includes conductive windings 54 so that relativemovement between the permanent magnets 52 on the rotor 48 and theconductive windings 54 on the stator 50 disrupts the magnetic field andinduces current flow in the conductive windings 54. One of ordinaryskill in the art will readily appreciate that the magnetic field may becreated by a current applied to the rotor 48 instead of permanentmagnets, or the stator 50 may generate the magnetic field, and the rotor48 may include the conductive windings 54, and the present invention isnot limited to the particular configuration of the electric generator 14unless specifically recited in the claims.

The electric generator 14 may be located outside of the shroud 20 orremote from the fluid flow path 24, and the present invention is notlimited to a particular location for the electric generator 14 unlessspecifically recited in the claims. In the particular embodiment shownin FIGS. 1-3, the electric generator 14 is located in the fluid flowpath 24 upstream from the gas turbine engine 12 and downstream from thepropulsor 18. In addition, the rotor 48 of the electric generator 14 iscoaxially aligned with the compressor 26, the turbine 30, and theturbine rotor 38 to avoid the need for gears or universal joints thatwould otherwise be needed to transfer rotational work from the gasturbine engine 12 to the electric generator 14.

The use of a gas turbine engine to drive an electric generator is knownin the art. For example, U.S. Pat. No. 6,962,057 describes a micro gasturbine in which a single-spool gas turbine engine drives a coaxiallyaligned electric generator to produce 20-100 kW of power. The poweroutput of the electric generator may be increased by increasing thestrength of the magnetic field, e.g., by incorporating larger permanentmagnets on the rotor. However, the additional mass associated withlarger permanent magnets produces larger centrifugal forces that tend toseparate the permanent magnets from the rotor, particularly at the highrotational speeds associated with a single-spool gas turbine engine thatdirectly drives the electric generator. Therefore, gas turbine enginesthat drive higher power output generators generally require multiplespools or shafts, gears, and/or transmissions that allow the electricgenerator to rotate at substantially lower speeds than the turbine inthe gas turbine engine to prevent the centrifugal forces from separatingthe permanent magnets from the rotor.

In the particular embodiment shown in FIGS. 1-3, the single spool orshaft 44 connects the turbine rotor 38 to the rotor 48 of the electricgenerator 14 so that the turbine rotor 38 and the generator rotor 48rotate at the same speed. Although the output power of the electricgenerator 14 is not a limitation of the present invention unless recitedin the claims, in particular embodiments, the electric generator 14 mayproduce an output of greater than 1 MW, 1.5 MW, or 2 MW. Inasmuch as theturbine rotor 38 may rotate at 20,000 rpm or more, the incorporation oflarger permanent magnets 52 on the rotor 48 to produce output powergreater than 1 MW requires additional structure to hold the permanentmagnets 52 in place. Therefore, the electric generator 14 may furtherinclude means for holding the permanent magnets 52 in place on the rotor48 during operation of the gas turbine engine 12, the turbine 30, and/orthe turbine rotor 38.

The function of the means for holding the permanent magnets 52 in placeon the rotor 48 during operation of the gas turbine engine 12, theturbine 30, and/or the turbine rotor 38 is to prevent movement betweenthe rotor 48 and the permanent magnets 52 during operations. Thestructure for performing this function may be any mechanical couplingwith the permanent magnets 52 that prevents the permanent magnets 52from moving with respect to the rotor 48. For example, the mechanicalcoupling may be one or more clamps, bolts, screws, or dovetail fittingsthat mechanically couple some or all of the permanent magnets 52 to therotor 48. Alternately, the mechanical coupling may be a series of railsor other projections that extend radially from the rotor 48 combinedwith an overwrap that circumferentially surrounds the permanent magnets52. The rails or other projections engage with some or all of thepermanent magnets 52 to transfer torque between the rotor 48 and thepermanent magnets 52 and prevent the permanent magnets 52 from movingcircumferentially with respect to the rotor 48. In particularembodiments, the rails or other projections may be contoured, ribbed,tapered, or flanged to match a complementary recess in the permanentmagnets 52. The overwrap that circumferentially surrounds the permanentmagnets 52 provides sufficient centripetal force against the permanentmagnets 52 to offset the centrifugal forces caused by rotation of therotor 48 to prevent the permanent magnets 52 from moving radially awayfrom the rotor 48. The overwrap may be a fiber or composite materialsprayed or wrapped around the outer circumference of the permanentmagnets 52. In combination, the rails or projections and overwrap thussecurely hold the permanent magnets 52 in contact with the rotor 48 toprevent circumferential and radial movement between the rotor 48 and thepermanent magnets 52 during operations.

FIG. 4 provides an axial cross-section view of the rotor 48 of theelectric generator 14 taken along line A-A of FIG. 3 according to oneembodiment of the present invention. In this particular embodiment, thepermanent magnets 52 are arranged circumferentially around the rotor 48and extend longitudinally along the rotor 48 to create the magneticfield. The means for holding the permanent magnets 52 in place on therotor 48 during operation of the gas turbine engine 12, the turbine 30,and/or the turbine rotor 38 includes multiple rails 56 and an overwrap58. The multiple rails 56 extend radially from the rotor 48 and mayextend longitudinally along some or all of the rotor 48. As shown inFIG. 4, the permanent magnets 52 are arranged in repeating groups 60 offour magnets 52, and the outer surface of the rotor 48 in contact withthe permanent magnets 52 is substantially flat. Three permanent magnets52 in each group 60 are sandwiched between or engaged with adjacentrails 56, and one permanent magnet 52 in each group 60 has a shorterradial dimension and is on top of a rail 56. In this manner, the rails56 provide the mechanical coupling between the rotor 48 and thepermanent magnets 52 to transfer torque between the rotor 48 and thepermanent magnets 52 and prevent the permanent magnets 52 from movingcircumferentially with respect to the rotor 48. The overwrap 58circumferentially surrounds the permanent magnets 52 to providesufficient centripetal force against the permanent magnets 52 to offsetthe centrifugal forces caused by rotation of the rotor 48 to prevent thepermanent magnets 52 from moving radially away from the rotor 48. Therails 56 and overwrap 58 thus combine to provide the structure forholding the permanent magnets 52 in place on the rotor 48 duringoperation of the gas turbine engine 12, the turbine 30, and/or theturbine rotor 38.

FIG. 5 provides an axial cross-section view of the rotor 48 of theelectric generator 14 taken along line A-A of FIG. 3 according to analternate embodiment of the present invention. As shown in FIG. 5, thepermanent magnets 52 are again arranged circumferentially around therotor 48 and extend longitudinally along the rotor 48 to create themagnetic field, and the means for holding the permanent magnets 52 inplace on the rotor 48 during operation of the gas turbine engine 12, theturbine 30, and/or the turbine rotor 38 again includes multiple rails 56and an overwrap 58 as described with respect to FIG. 4. The permanentmagnets 52 are again arranged in eight repeating groups 60 of fourmagnets 52. In this particular embodiment, however, the outer surface ofthe rotor 48 in contact with the permanent magnets 52 is curved, withthe magnitude of the curve based on the radius of the rotor 48. As aresult, this particular embodiment only requires fabrication of twodifferent magnet sizes. Specifically, the three permanent magnets 52 ineach group 60 that are sandwiched between or engaged with adjacent rails56 are identical to one another, and the permanent magnet 52 in eachgroup 60 on top of a rail 56 differs only in its radial dimension. Theuse of substantially identical permanent magnets 52 simplifiesconstruction by reducing the manufacturing and maintenance costsassociated with the permanent magnets 52.

FIG. 6 provides an axial cross-section view of the rotor 48 of theelectric generator 14 taken along line A-A of FIG. 3 according to analternate embodiment of the present invention. As shown in FIG. 6, thepermanent magnets 52 are again arranged circumferentially around therotor 48 and extend longitudinally along the rotor 48 to create themagnetic field, and the means for holding the permanent magnets 52 inplace on the rotor 48 during operation of the gas turbine engine 12, theturbine 30, and/or the turbine rotor 38 again includes multiple rails 56and an overwrap 58 as described with respect to FIG. 4. In thisparticular embodiment, the means further includes a recess 62 in some orall of the permanent magnets 52. Each recess 62 may have a shape that iscomplementary to the shape of the rails 56 to allow each rail 56 toextend into a recess 62 of a different permanent magnet 52. Themechanical coupling between the rails 56 and recesses 62 prevents thepermanent magnets 52 from moving circumferentially with respect to therotor 48, and the overwrap 58 prevents the permanent magnets 52 frommoving radially away from the rotor 48. The rails 56, recesses 62, andoverwrap 58 thus combine to provide the structure for holding thepermanent magnets 52 in place on the rotor 48 during operation of thegas turbine engine 12, the turbine 30, and/or the turbine rotor 38.

FIG. 7 provides an axial cross-section view of the rotor 48 of theelectric generator 14 taken along line A-A of FIG. 3 according to analternate embodiment of the present invention. As shown in FIG. 7, themeans for holding the permanent magnets 52 in place on the rotor 48during operation of the gas turbine engine 12, the turbine 30, and/orthe turbine rotor 38 again includes multiple rails 56 and recesses 62 inthe permanent magnets 52. In this particular embodiment, the rails 56are T-shaped, and the recesses 62 in the permanent magnets 52 have acomplementary shape to receive the T-shaped rails 56. The rails 56 andrecesses 62 thus provide the mechanical coupling that prevents thepermanent magnets 52 from moving both circumferentially and radiallywith respect to the rotor 48, and an overwrap is not needed in thisembodiment to perform the function of holding the permanent magnets 52in place on the rotor 48 during operation of the gas turbine engine 12,the turbine 30, and/or the turbine rotor 38. One of ordinary skill inthe art will readily appreciate that other shapes for the rails 56 andrecesses 62 would similarly perform the function of holding thepermanent magnets 52 in place on the rotor 48 during operation of thegas turbine engine 12, the turbine 30, and/or the turbine rotor 38without the need for an overwrap. For example, alternate embodiments ofthe present invention may include rails 56 and recesses 62 having a firtree shape, an L-shape, a dovetail shape, etc., and the presentinvention is not limited to any particular shape for the rails 56 andrecesses 62 unless specifically recited in the claims.

The embodiments shown in FIGS. 4-7 thus allow larger and heavierpermanent magnets 52 to be incorporated into the electric generator 14to increase the output power of the electric generator 14. For example,embodiments in which the single spool or shaft 44 rotates the rotor 48of the electric generator 14 at the same speed as the turbine rotor 38may generate an output of more than 1 MW, 1.5 MW, or even 2 MW,depending on the radius of the rotor 48 and the size of the permanentmagnets 52. This substantial output power may be used for any purpose,such as providing a portable power supply to remote geographic areas orfollowing weather-related catastrophes.

Alternately, as shown in FIG. 1, the electric generator 14 may beincorporated into the gas turbine propulsion system 10 to provideelectric power to drive the electric motor 16 of the propulsor 18. Asshown by the dashed lines of FIG. 1, the output from the electricgenerator 14 may be routed to an electric bus 64. In this manner, theelectric bus 64 may supply electric power to the electric motor 16 todrive the propulsor 18 or to a storage device, such as a battery 66, forsubsequent use by the electric motor 16 to drive the propulsor 18 whenthe gas turbine engine 12 is not operating.

FIGS. 8 and 9 provide enlarged side and perspective cross-section viewsof the electric motor 16 and propulsor 18 shown in FIG. 1. As shown inFIG. 1, a casing 68 may surround the electric generator 14 and electricmotor 16 to minimize disruption in the fluid flow path 24 between theelectric generator 14 and electric motor 16. However, the electric motor16 and propulsor 18 are rotationally isolated from the gas turbineengine 12 so that the propulsor 18 rotates independently from operationof the gas turbine engine 12 at all times.

The electric motor 16 provides the sole driving force for the propulsor18. The electric motor 16 generally includes a rotor 70 and a stator 72,and current flow disrupts a magnetic field between the two to convertelectrical energy into mechanical energy, as is known in the art. In theparticular embodiment shown in FIGS. 8 and 9, the rotor 70 provides themagnetic field, and the stator 72 includes conductive windings so thatcurrent flow through the stator 72 disrupts the magnetic field andinduces rotational movement in the rotor 70. One of ordinary skill inthe art will readily appreciate that the stator 72 may generate themagnetic field, and the rotor 70 may include the conductive windings,and the present invention is not limited to the particular configurationof the electric motor 16 unless specifically recited in the claims.

The electric motor 16 may be located outside of the shroud 20 or remotefrom the fluid flow path 24, and the present invention is not limited toa particular location for the electric motor 16 unless specificallyrecited in the claims. In the particular embodiment shown in FIGS. 1, 8,and 9, the electric motor 16 is located in the fluid flow path 24upstream from the gas turbine engine 12 and downstream from thepropulsor 18. A shaft 74 couples the rotor 70 to the propulsor 18, andthe rotor 70 is coaxially aligned with the propulsor 18 to avoid theneed for gears or universal joints that would otherwise be needed totransfer rotational work from the electric motor 16 to the propulsor 18.

The propulsor 18 may be a propeller that rotates outside of the shroud20 or a fan enclosed by the shroud 20 or cowling. In either event, thepropulsor 18 may be either axially offset from or coaxially aligned withthe gas turbine engine 12 and/or electric motor 16, depending on theparticular design. In the particular embodiment shown in FIGS. 1, 8, and9, the propulsor 18 is a fan 76 surrounded by the shroud 20 or cowlingand coaxially aligned with the electric motor 16 and gas turbine engine12. Rotation of the fan 76 increases the pressure and velocity of air inthe fluid flow path 24. As a result, air from the fluid flow path 24entering the compressor 26 is supercharged, increasing the efficiency ofthe gas turbine engine 12. In particular embodiments, the increasedefficiency on the gas turbine engine 12 may allow for a reduction in theturbine inlet temperature of approximately 150 degrees Fahrenheit orproduce an increase of approximately 200 kW for the same turbine inlettemperature.

Referring again to FIG. 1, the rotational isolation between the gasturbine engine 12 and the propulsor 18 allows the gas turbine propulsionsystem 10 to operate in multiple modes, depending on the particularoperational needs. For example, the efficiency of the gas turbinepropulsion system 10 may be optimized by operating the gas turbineengine 12 at its most efficient power level and varying the power levelor speed of the propulsor 18 as needed to produce a desired amount ofthrust. In this operating mode, the gas turbine engine 12 drives theelectric generator 14 to produce 1 MW, 1.5 MW, 2 MW, or more of electricpower which is then supplied through the electric bus 64 to either theelectric motor 16 to drive the propulsor 18 or to the battery 66. Asanother example, the sound signature of the gas turbine propulsionsystem 10 may be minimized by operating the propulsor 18 with the gasturbine engine 12 secured. The electric bus 64 may supply electric powerfrom the battery 66 to the electric motor 16 to drive the propulsor 18to produce a desired amount of thrust.

The embodiments previously described and illustrated with respect toFIGS. 1-7 may also provide a method for starting the gas turbine engine12 without requiring a separate starter motor. For example, the electricbus 64 may supply electric power from the battery 66 or an externalsource of power to the electric generator 14, causing the electricgenerator 14 to act as an electric motor. The single spool or shaft 44then transmits rotation from the generator rotor 48 to the compressorrotor 32 and turbine rotor 38. The combustors 28 may be ignited once thecompressor rotor 32 and turbine rotor 38 reach a minimum sustainedspeed, typically approximately 15% of idle speed. Electric power to theelectric generator 14 and fuel flow to the combustors 28 may begradually increased until the combustors can provide sufficientcombustion gases to the turbine 30 to achieve a self-sustaining speedfor the gas turbine engine 12, typically approximately 50% of idlespeed. At the self-sustaining speed, the single spool or shaft 44 againtransmits rotation from the turbine rotor 38 to the generator rotor 48as the turbine 30 accelerates to the steady state operating speed ofapproximately 100%. At this speed, the electric generator 14 may beconnected to a load or power electronics to produce electric output.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal language of the claims.

What is claimed is:
 1. A power generation system, comprising: a shroudthat defines a fluid flow path; a compressor in said fluid flow path; acombustor in said fluid flow path downstream from said compressor; aturbine in said fluid flow path downstream from said compressor and saidcombustor; an electric generator in said fluid flow path upstream fromsaid compressor, wherein said electric generator comprises a rotorcoaxially aligned with said turbine; and a shaft that connects saidturbine to said rotor of said electric generator.
 2. The powergeneration system as in claim 1, wherein said turbine comprises anintegrally bladed rotor.
 3. The power generation system as in claim 1,wherein said electric generator is configured to generate at least 1megawatt of output power.
 4. The power generation system as in claim 1,wherein said electric generator comprises means for holding a pluralityof permanent magnets in place on said rotor of said electric generatorduring operation of said turbine.
 5. The power generation system as inclaim 4, wherein said means for holding a plurality of permanent magnetsin place on said rotor of said electric generator during operation ofsaid turbine comprises a plurality of rails that extend radially fromsaid rotor of said electric generator and engage with said plurality ofpermanent magnets.
 6. The power generation system as in claim 5, whereinsaid means for holding a plurality of permanent magnets in place on saidrotor of said electric generator during operation of said turbinefurther comprises an overwrap that circumferentially surrounds saidplurality of permanent magnets.
 7. The power generation system as inclaim 4, wherein said means for holding a plurality of permanent magnetsin place on said rotor of said electric generator during operation ofsaid turbine comprises a plurality of rails that extend radially fromsaid rotor of said electric generator, a recess in each of saidplurality of permanent magnets, and each rail of said plurality of railsextends into said recess of a different permanent magnet of saidplurality of magnets.
 8. The power generation system as in claim 1,wherein said turbine and said rotor rotate at the same speed.
 9. Thepower generation system as in claim 1, further comprising a plurality ofnon-lubricated bearings that rotatably support said shaft.
 10. A powergeneration system, comprising: a gas turbine engine, wherein said gasturbine engine comprises a compressor, a combustor downstream from saidcompressor, and a turbine downstream from said combustor; an electricgenerator coaxially aligned with said compressor, wherein said electricgenerator comprises a rotor coaxially aligned with said turbine; a shaftthat connects said turbine of said gas turbine engine to said rotor ofsaid electric generator; wherein said electric generator comprises meansfor holding a plurality of permanent magnets in place on said rotor ofsaid electric generator during operation of said turbine.
 11. The powergeneration system as in claim 10, wherein said turbine of said gasturbine engine comprises an integrally bladed rotor.
 12. The powergeneration system as in claim 10, wherein said electric generator isconfigured to generate at least 1 megawatt of output power.
 13. Thepower generation system as in claim 10, wherein said means for holding aplurality of permanent magnets in place on said rotor of said electricgenerator during operation of said turbine comprises a plurality ofrails that extend radially from said rotor of said electric generatorand engage with said plurality of permanent magnets.
 14. The powergeneration system as in claim 13, wherein said means for holding aplurality of permanent magnets in place on said rotor of said electricgenerator during operation of said turbine further comprises an overwrapthat circumferentially surrounds said plurality of permanent magnets.15. The power generation system as in claim 10, wherein said means forholding a plurality of permanent magnets in place on said rotor of saidelectric generator during operation of said turbine comprises aplurality of rails that extend radially from said rotor of said electricgenerator, a recess in each of said plurality of permanent magnets, andeach rail of said plurality of rails extends into said recess of adifferent permanent magnet of said plurality of magnets.
 16. The powergeneration system as in claim 10, further comprising a plurality ofnon-lubricated bearings that rotatably support said shaft.
 17. A powergeneration system, comprising: a gas turbine engine, wherein said gasturbine engine comprises a compressor, a combustor downstream from saidcompressor, and a turbine downstream from said combustor; an electricgenerator coaxially aligned with said turbine, wherein said electricgenerator comprises a rotor; a shaft that connects said turbine of saidgas turbine engine to said rotor of said electric generator; a pluralityof rails that extend radially from said rotor of said electricgenerator; and a plurality of permanent magnets engaged with saidplurality of rails.
 18. The power generation system as in claim 17,wherein said electric generator is configured to generate at least 1megawatt of output power.
 19. The power generation system as in claim17, further comprising an overwrap that circumferentially surrounds saidplurality of permanent magnets.
 20. The power generation system as inclaim 17, further comprising a recess in each of said plurality ofpermanent magnets, wherein each rail of said plurality of rails extendsinto said recess of a different permanent magnet of said plurality ofmagnets.